Protection by two complexing agents, thiosulphate and dissolved organic matter, against the physiological effects of silver nitrate to rainbow trout (Oncorhynchus mykiss) in ion-poor water

Adult rainbow trout (Oncorhynchus mykiss) were exposed in ion-poor water (s imilar to 50 mu M Ca) to silver added as AgNO3 or to AgNO3 plus either thio sulphate (Na2S2O3) pr dissolved organic matter (DOM). The effects of these exposures were assessed through repetitive blood sampling over 4 days. Trou t exposed to 0.1 mu M AgNO3 alone accumulated large amounts of Ag on their gills and in their plasma, showed progressive losses of plasma Ma and Cl, a nd had elevated concentrations of plasma glucose. In one set of exposures t rout exposed to AgNO3 alone also had increased cough rates, slightly higher ventilation rates, somewhat lower arterial oxygen tensions, and increased blood lactate concentrations. In contrast, trout exposed to 0.1 mu M AgNO3 plus 5 mu M thiosulphate or 35 mg C l(-1) DOM accumulated less Ag on their gills and in their plasma, and showed no adverse ionoregulatory or respirat ory effects due to Ag. These results demonstrate ionoregulatory and sometim es respiratory effects in fish exposed to ionic Ag+ in ion-poor water, depe nding on water chemistry, and demonstrate the protective effects of synthet ic and natural complexing agents through a reduction in the amount of ionic Ag+ available to bind at the gills. O 2000 Elsevier Science B.V. All right s reserved.